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<pre><span class="sourceLineNo">001</span><a name="line.1"></a>
<span class="sourceLineNo">002</span>/*<a name="line.2"></a>
<span class="sourceLineNo">003</span> * Copyright (C) 2011 Archie L. Cobbs. All rights reserved.<a name="line.3"></a>
<span class="sourceLineNo">004</span> *<a name="line.4"></a>
<span class="sourceLineNo">005</span> * $Id: IdGenerator.html 689 2013-06-28 19:22:16Z archie.cobbs $<a name="line.5"></a>
<span class="sourceLineNo">006</span> */<a name="line.6"></a>
<span class="sourceLineNo">007</span><a name="line.7"></a>
<span class="sourceLineNo">008</span>package org.dellroad.stuff.java;<a name="line.8"></a>
<span class="sourceLineNo">009</span><a name="line.9"></a>
<span class="sourceLineNo">010</span>import java.lang.ref.Reference;<a name="line.10"></a>
<span class="sourceLineNo">011</span>import java.lang.ref.ReferenceQueue;<a name="line.11"></a>
<span class="sourceLineNo">012</span>import java.lang.ref.WeakReference;<a name="line.12"></a>
<span class="sourceLineNo">013</span>import java.util.HashMap;<a name="line.13"></a>
<span class="sourceLineNo">014</span>import java.util.concurrent.Callable;<a name="line.14"></a>
<span class="sourceLineNo">015</span><a name="line.15"></a>
<span class="sourceLineNo">016</span>/**<a name="line.16"></a>
<span class="sourceLineNo">017</span> * Registry of unique IDs for objects.<a name="line.17"></a>
<span class="sourceLineNo">018</span> *<a name="line.18"></a>
<span class="sourceLineNo">019</span> * &lt;p&gt;<a name="line.19"></a>
<span class="sourceLineNo">020</span> * Instances support creating unique {@code long} ID numbers for objects, as well as setting the unique ID<a name="line.20"></a>
<span class="sourceLineNo">021</span> * to a specific value for any unregistered object.<a name="line.21"></a>
<span class="sourceLineNo">022</span> *<a name="line.22"></a>
<span class="sourceLineNo">023</span> * &lt;p&gt;<a name="line.23"></a>
<span class="sourceLineNo">024</span> * This class uses object identity, not {@link Object#equals Object.equals()}, to distinguish objects.<a name="line.24"></a>
<span class="sourceLineNo">025</span> *<a name="line.25"></a>
<span class="sourceLineNo">026</span> * &lt;p&gt;<a name="line.26"></a>
<span class="sourceLineNo">027</span> * Weak references are used to ensure that registered objects can be garbage collected normally.<a name="line.27"></a>
<span class="sourceLineNo">028</span> *<a name="line.28"></a>
<span class="sourceLineNo">029</span> * &lt;p&gt;<a name="line.29"></a>
<span class="sourceLineNo">030</span> * New {@code long} ID numbers are issued serially; after 2&lt;sup&gt;64&lt;/sup&gt;-1 invocations of {@link #getId getId()},<a name="line.30"></a>
<span class="sourceLineNo">031</span> * an {@link IllegalStateException} will be thrown.<a name="line.31"></a>
<span class="sourceLineNo">032</span> *<a name="line.32"></a>
<span class="sourceLineNo">033</span> * @see org.dellroad.stuff.jibx.IdMapper<a name="line.33"></a>
<span class="sourceLineNo">034</span> */<a name="line.34"></a>
<span class="sourceLineNo">035</span>public class IdGenerator {<a name="line.35"></a>
<span class="sourceLineNo">036</span><a name="line.36"></a>
<span class="sourceLineNo">037</span>    private static final ThreadLocalHolder&lt;IdGenerator&gt; CURRENT = new ThreadLocalHolder&lt;IdGenerator&gt;();<a name="line.37"></a>
<span class="sourceLineNo">038</span><a name="line.38"></a>
<span class="sourceLineNo">039</span>    private final HashMap&lt;Ref, Long&gt; idMap = new HashMap&lt;Ref, Long&gt;();<a name="line.39"></a>
<span class="sourceLineNo">040</span>    private final HashMap&lt;Long, Ref&gt; refMap = new HashMap&lt;Long, Ref&gt;();<a name="line.40"></a>
<span class="sourceLineNo">041</span>    private final ReferenceQueue&lt;Object&gt; queue = new ReferenceQueue&lt;Object&gt;();<a name="line.41"></a>
<span class="sourceLineNo">042</span><a name="line.42"></a>
<span class="sourceLineNo">043</span>    private long next = 1;<a name="line.43"></a>
<span class="sourceLineNo">044</span><a name="line.44"></a>
<span class="sourceLineNo">045</span>    /**<a name="line.45"></a>
<span class="sourceLineNo">046</span>     * Get a unique ID for the given object.<a name="line.46"></a>
<span class="sourceLineNo">047</span>     *<a name="line.47"></a>
<span class="sourceLineNo">048</span>     * &lt;p&gt;<a name="line.48"></a>
<span class="sourceLineNo">049</span>     * If this method has been previously invoked on this instance with the same {@code obj} parameter (where "same" means<a name="line.49"></a>
<span class="sourceLineNo">050</span>     * object identity, not {@link Object#equals Object.equals()} identity), then the same ID value will be returned.<a name="line.50"></a>
<span class="sourceLineNo">051</span>     * Otherwise a new ID value will be returned.<a name="line.51"></a>
<span class="sourceLineNo">052</span>     *<a name="line.52"></a>
<span class="sourceLineNo">053</span>     * &lt;p&gt;<a name="line.53"></a>
<span class="sourceLineNo">054</span>     * New IDs are assigned sequentially starting at {@code 1}. No conflict avoidance with IDs assigned<a name="line.54"></a>
<span class="sourceLineNo">055</span>     * via {@link #setId setId()} is performed; if there is a conflict, an exception is thrown.<a name="line.55"></a>
<span class="sourceLineNo">056</span>     *<a name="line.56"></a>
<span class="sourceLineNo">057</span>     * @throws IllegalArgumentException if {@code obj} is null<a name="line.57"></a>
<span class="sourceLineNo">058</span>     * @throws IllegalStateException if the next sequential ID has already been assigned to a different object<a name="line.58"></a>
<span class="sourceLineNo">059</span>     *  via {@link #setId setId()}<a name="line.59"></a>
<span class="sourceLineNo">060</span>     * @throws IllegalStateException if all 2&lt;sup&gt;64&lt;/sup&gt;-1 values have been used up<a name="line.60"></a>
<span class="sourceLineNo">061</span>     * @return a non-zero, unique identifier for {@code obj}<a name="line.61"></a>
<span class="sourceLineNo">062</span>     */<a name="line.62"></a>
<span class="sourceLineNo">063</span>    public synchronized long getId(Object obj) {<a name="line.63"></a>
<span class="sourceLineNo">064</span>        if (obj == null)<a name="line.64"></a>
<span class="sourceLineNo">065</span>            throw new IllegalArgumentException("null obj");<a name="line.65"></a>
<span class="sourceLineNo">066</span>        this.flush();<a name="line.66"></a>
<span class="sourceLineNo">067</span>        Long id = this.idMap.get(new Ref(obj));         // don't register on queue just yet<a name="line.67"></a>
<span class="sourceLineNo">068</span>        if (id == null) {<a name="line.68"></a>
<span class="sourceLineNo">069</span>            if (this.next == 0)<a name="line.69"></a>
<span class="sourceLineNo">070</span>                throw new IllegalStateException("no more identifiers left!");<a name="line.70"></a>
<span class="sourceLineNo">071</span>            Ref ref = new Ref(obj, this.queue);             // now register on queue<a name="line.71"></a>
<span class="sourceLineNo">072</span>            id = this.next++;<a name="line.72"></a>
<span class="sourceLineNo">073</span>            this.idMap.put(ref, id);<a name="line.73"></a>
<span class="sourceLineNo">074</span>            this.refMap.put(id, ref);<a name="line.74"></a>
<span class="sourceLineNo">075</span>        }<a name="line.75"></a>
<span class="sourceLineNo">076</span>        return id;<a name="line.76"></a>
<span class="sourceLineNo">077</span>    }<a name="line.77"></a>
<span class="sourceLineNo">078</span><a name="line.78"></a>
<span class="sourceLineNo">079</span>    /**<a name="line.79"></a>
<span class="sourceLineNo">080</span>     * Test whether the given object is already registered with this instance.<a name="line.80"></a>
<span class="sourceLineNo">081</span>     *<a name="line.81"></a>
<span class="sourceLineNo">082</span>     * @throws IllegalArgumentException if {@code obj} is null<a name="line.82"></a>
<span class="sourceLineNo">083</span>     * @return a non-zero, unique identifier for {@code obj} if already registered, otherwise zero<a name="line.83"></a>
<span class="sourceLineNo">084</span>     */<a name="line.84"></a>
<span class="sourceLineNo">085</span>    public synchronized long checkId(Object obj) {<a name="line.85"></a>
<span class="sourceLineNo">086</span>        if (obj == null)<a name="line.86"></a>
<span class="sourceLineNo">087</span>            throw new IllegalArgumentException("null obj");<a name="line.87"></a>
<span class="sourceLineNo">088</span>        this.flush();<a name="line.88"></a>
<span class="sourceLineNo">089</span>        Long id = this.idMap.get(new Ref(obj));<a name="line.89"></a>
<span class="sourceLineNo">090</span>        return id != null ? id : 0;<a name="line.90"></a>
<span class="sourceLineNo">091</span>    }<a name="line.91"></a>
<span class="sourceLineNo">092</span><a name="line.92"></a>
<span class="sourceLineNo">093</span>    /**<a name="line.93"></a>
<span class="sourceLineNo">094</span>     * Assign a unique ID to the given object. Does nothing if the object and ID number are already associated.<a name="line.94"></a>
<span class="sourceLineNo">095</span>     *<a name="line.95"></a>
<span class="sourceLineNo">096</span>     * @param obj object to assign<a name="line.96"></a>
<span class="sourceLineNo">097</span>     * @param id unique ID number to assign<a name="line.97"></a>
<span class="sourceLineNo">098</span>     * @throws IllegalArgumentException if {@code obj} is null<a name="line.98"></a>
<span class="sourceLineNo">099</span>     * @throws IllegalArgumentException if {@code id} has already been assigned to some other object<a name="line.99"></a>
<span class="sourceLineNo">100</span>     */<a name="line.100"></a>
<span class="sourceLineNo">101</span>    public synchronized void setId(Object obj, long id) {<a name="line.101"></a>
<span class="sourceLineNo">102</span>        if (obj == null)<a name="line.102"></a>
<span class="sourceLineNo">103</span>            throw new IllegalArgumentException("null obj");<a name="line.103"></a>
<span class="sourceLineNo">104</span>        this.flush();<a name="line.104"></a>
<span class="sourceLineNo">105</span>        Ref ref = this.refMap.get(id);<a name="line.105"></a>
<span class="sourceLineNo">106</span>        if (ref != null) {<a name="line.106"></a>
<span class="sourceLineNo">107</span>            if (ref.get() != obj)<a name="line.107"></a>
<span class="sourceLineNo">108</span>                throw new IllegalArgumentException("id " + id + " is already assigned to another object");<a name="line.108"></a>
<span class="sourceLineNo">109</span>            return;<a name="line.109"></a>
<span class="sourceLineNo">110</span>        }<a name="line.110"></a>
<span class="sourceLineNo">111</span>        ref = new Ref(obj, this.queue);<a name="line.111"></a>
<span class="sourceLineNo">112</span>        this.idMap.put(ref, id);<a name="line.112"></a>
<span class="sourceLineNo">113</span>        this.refMap.put(id, ref);<a name="line.113"></a>
<span class="sourceLineNo">114</span>    }<a name="line.114"></a>
<span class="sourceLineNo">115</span><a name="line.115"></a>
<span class="sourceLineNo">116</span>    /**<a name="line.116"></a>
<span class="sourceLineNo">117</span>     * Get the object assigned to the given ID.<a name="line.117"></a>
<span class="sourceLineNo">118</span>     *<a name="line.118"></a>
<span class="sourceLineNo">119</span>     * @param id unique ID<a name="line.119"></a>
<span class="sourceLineNo">120</span>     * @return object associated with that ID, or null if no object is assigned to {@code id}<a name="line.120"></a>
<span class="sourceLineNo">121</span>     */<a name="line.121"></a>
<span class="sourceLineNo">122</span>    public synchronized Object getObject(long id) {<a name="line.122"></a>
<span class="sourceLineNo">123</span>        this.flush();<a name="line.123"></a>
<span class="sourceLineNo">124</span>        Ref ref = this.refMap.get(id);<a name="line.124"></a>
<span class="sourceLineNo">125</span>        return ref != null ? ref.get() : null;<a name="line.125"></a>
<span class="sourceLineNo">126</span>    }<a name="line.126"></a>
<span class="sourceLineNo">127</span><a name="line.127"></a>
<span class="sourceLineNo">128</span>    /**<a name="line.128"></a>
<span class="sourceLineNo">129</span>     * Flush any cleared weak references.<a name="line.129"></a>
<span class="sourceLineNo">130</span>     *<a name="line.130"></a>
<span class="sourceLineNo">131</span>     * &lt;p&gt;<a name="line.131"></a>
<span class="sourceLineNo">132</span>     * This operation is invoked by {@link #getId getId()} and {@link #setId setId()}, so it's usually not necessary<a name="line.132"></a>
<span class="sourceLineNo">133</span>     * to explicitly invoke it. However, if a lot of previously ID'd objects have been garbage collected since the<a name="line.133"></a>
<span class="sourceLineNo">134</span>     * last call to {@link #getId getId()}, then invoking this method may free up some additional memory.<a name="line.134"></a>
<span class="sourceLineNo">135</span>     */<a name="line.135"></a>
<span class="sourceLineNo">136</span>    public synchronized void flush() {<a name="line.136"></a>
<span class="sourceLineNo">137</span>        Reference&lt;? extends Object&gt; entry;<a name="line.137"></a>
<span class="sourceLineNo">138</span>        while ((entry = this.queue.poll()) != null) {<a name="line.138"></a>
<span class="sourceLineNo">139</span>            Ref ref = (Ref)entry;<a name="line.139"></a>
<span class="sourceLineNo">140</span>            Long id = this.idMap.get(ref);<a name="line.140"></a>
<span class="sourceLineNo">141</span>            this.idMap.remove(ref);<a name="line.141"></a>
<span class="sourceLineNo">142</span>            this.refMap.remove(id);<a name="line.142"></a>
<span class="sourceLineNo">143</span>        }<a name="line.143"></a>
<span class="sourceLineNo">144</span>    }<a name="line.144"></a>
<span class="sourceLineNo">145</span><a name="line.145"></a>
<span class="sourceLineNo">146</span>    /**<a name="line.146"></a>
<span class="sourceLineNo">147</span>     * Create a new {@link IdGenerator} and make it available via {@link #get()} for the duration of the given operation.<a name="line.147"></a>
<span class="sourceLineNo">148</span>     *<a name="line.148"></a>
<span class="sourceLineNo">149</span>     * &lt;p&gt;<a name="line.149"></a>
<span class="sourceLineNo">150</span>     * This method is re-entrant: nested invocations of this method in the same thread re-use the same {@link IdGenerator}<a name="line.150"></a>
<span class="sourceLineNo">151</span>     * instance.<a name="line.151"></a>
<span class="sourceLineNo">152</span>     *<a name="line.152"></a>
<span class="sourceLineNo">153</span>     * @param action action to perform, and which may successfully invoke {@link #get}<a name="line.153"></a>
<span class="sourceLineNo">154</span>     * @throws NullPointerException if {@code action} is null<a name="line.154"></a>
<span class="sourceLineNo">155</span>     */<a name="line.155"></a>
<span class="sourceLineNo">156</span>    public static void run(final Runnable action) {<a name="line.156"></a>
<span class="sourceLineNo">157</span>        IdGenerator current = IdGenerator.CURRENT.get();<a name="line.157"></a>
<span class="sourceLineNo">158</span>        if (current == null)<a name="line.158"></a>
<span class="sourceLineNo">159</span>            current = new IdGenerator();<a name="line.159"></a>
<span class="sourceLineNo">160</span>        IdGenerator.CURRENT.invoke(current, action);<a name="line.160"></a>
<span class="sourceLineNo">161</span>    }<a name="line.161"></a>
<span class="sourceLineNo">162</span><a name="line.162"></a>
<span class="sourceLineNo">163</span>    /**<a name="line.163"></a>
<span class="sourceLineNo">164</span>     * Create a new {@link IdGenerator} and make it available via {@link #get()} for the duration of the given operation.<a name="line.164"></a>
<span class="sourceLineNo">165</span>     *<a name="line.165"></a>
<span class="sourceLineNo">166</span>     * &lt;p&gt;<a name="line.166"></a>
<span class="sourceLineNo">167</span>     * This method is re-entrant: nested invocations of this method in the same thread re-use the same {@link IdGenerator}<a name="line.167"></a>
<span class="sourceLineNo">168</span>     * instance.<a name="line.168"></a>
<span class="sourceLineNo">169</span>     *<a name="line.169"></a>
<span class="sourceLineNo">170</span>     * @param action action to perform, and which may successfully invoke {@link #get}<a name="line.170"></a>
<span class="sourceLineNo">171</span>     * @return result of invoking {@code action}<a name="line.171"></a>
<span class="sourceLineNo">172</span>     * @throws NullPointerException if {@code action} is null<a name="line.172"></a>
<span class="sourceLineNo">173</span>     */<a name="line.173"></a>
<span class="sourceLineNo">174</span>    public static &lt;R&gt; R run(final Callable&lt;R&gt; action) throws Exception {<a name="line.174"></a>
<span class="sourceLineNo">175</span>        IdGenerator current = IdGenerator.CURRENT.get();<a name="line.175"></a>
<span class="sourceLineNo">176</span>        if (current == null)<a name="line.176"></a>
<span class="sourceLineNo">177</span>            current = new IdGenerator();<a name="line.177"></a>
<span class="sourceLineNo">178</span>        return IdGenerator.CURRENT.invoke(current, action);<a name="line.178"></a>
<span class="sourceLineNo">179</span>    }<a name="line.179"></a>
<span class="sourceLineNo">180</span><a name="line.180"></a>
<span class="sourceLineNo">181</span>    /**<a name="line.181"></a>
<span class="sourceLineNo">182</span>     * Get the {@link IdGenerator} associated with the current thread.<a name="line.182"></a>
<span class="sourceLineNo">183</span>     * This method only works when the current thread is running within an invocation of {@link #run run()};<a name="line.183"></a>
<span class="sourceLineNo">184</span>     * otherwise, an {@link IllegalStateException} is thrown.<a name="line.184"></a>
<span class="sourceLineNo">185</span>     *<a name="line.185"></a>
<span class="sourceLineNo">186</span>     * @return the {@link IdGenerator} created in the most recent, still running invocation of {@link #run} in this thread<a name="line.186"></a>
<span class="sourceLineNo">187</span>     * @throws IllegalStateException if there is not such instance<a name="line.187"></a>
<span class="sourceLineNo">188</span>     */<a name="line.188"></a>
<span class="sourceLineNo">189</span>    public static IdGenerator get() {<a name="line.189"></a>
<span class="sourceLineNo">190</span>        return IdGenerator.CURRENT.require();<a name="line.190"></a>
<span class="sourceLineNo">191</span>    }<a name="line.191"></a>
<span class="sourceLineNo">192</span><a name="line.192"></a>
<span class="sourceLineNo">193</span>// Reference to a registered object that weakly references the actual object<a name="line.193"></a>
<span class="sourceLineNo">194</span><a name="line.194"></a>
<span class="sourceLineNo">195</span>    private static final class Ref extends WeakReference&lt;Object&gt; {<a name="line.195"></a>
<span class="sourceLineNo">196</span><a name="line.196"></a>
<span class="sourceLineNo">197</span>        private final int hashCode;<a name="line.197"></a>
<span class="sourceLineNo">198</span><a name="line.198"></a>
<span class="sourceLineNo">199</span>        Ref(Object obj, ReferenceQueue&lt;Object&gt; queue) {<a name="line.199"></a>
<span class="sourceLineNo">200</span>            super(obj, queue);<a name="line.200"></a>
<span class="sourceLineNo">201</span>            if (obj == null)<a name="line.201"></a>
<span class="sourceLineNo">202</span>                throw new IllegalArgumentException("null obj");<a name="line.202"></a>
<span class="sourceLineNo">203</span>            this.hashCode = System.identityHashCode(obj);<a name="line.203"></a>
<span class="sourceLineNo">204</span>        }<a name="line.204"></a>
<span class="sourceLineNo">205</span><a name="line.205"></a>
<span class="sourceLineNo">206</span>        Ref(Object obj) {<a name="line.206"></a>
<span class="sourceLineNo">207</span>            this(obj, null);<a name="line.207"></a>
<span class="sourceLineNo">208</span>        }<a name="line.208"></a>
<span class="sourceLineNo">209</span><a name="line.209"></a>
<span class="sourceLineNo">210</span>        @Override<a name="line.210"></a>
<span class="sourceLineNo">211</span>        public boolean equals(Object obj) {<a name="line.211"></a>
<span class="sourceLineNo">212</span>            if (obj == this)<a name="line.212"></a>
<span class="sourceLineNo">213</span>                return true;<a name="line.213"></a>
<span class="sourceLineNo">214</span>            if (obj == null || obj.getClass() != this.getClass())<a name="line.214"></a>
<span class="sourceLineNo">215</span>                return false;<a name="line.215"></a>
<span class="sourceLineNo">216</span>            Ref that = (Ref)obj;<a name="line.216"></a>
<span class="sourceLineNo">217</span>            obj = this.get();<a name="line.217"></a>
<span class="sourceLineNo">218</span>            return obj != null ? obj == that.get() : false;<a name="line.218"></a>
<span class="sourceLineNo">219</span>        }<a name="line.219"></a>
<span class="sourceLineNo">220</span><a name="line.220"></a>
<span class="sourceLineNo">221</span>        @Override<a name="line.221"></a>
<span class="sourceLineNo">222</span>        public int hashCode() {<a name="line.222"></a>
<span class="sourceLineNo">223</span>            return this.hashCode;<a name="line.223"></a>
<span class="sourceLineNo">224</span>        }<a name="line.224"></a>
<span class="sourceLineNo">225</span>    }<a name="line.225"></a>
<span class="sourceLineNo">226</span>}<a name="line.226"></a>
<span class="sourceLineNo">227</span><a name="line.227"></a>




























































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